1. Field of the Invention
The present invention relates to current perpendicular to the plane (hereinafter referred to as “CPP”) type magnetic sensors in which a sense current is allowed to flow in a direction perpendicular to a film surface, and more particularly, relates to a magnetic sensor being able to increase ΔR·A, that is, the product of a change ΔR in resistance and an element area A.
2. Description of the Related Art
FIG. 7 is a partial cross-sectional view of a related magnetic sensor (spin valve thin film element) taken along a direction parallel to a face facing a recording medium.
Reference numeral 1 shown in FIG. 7 indicates an underlayer made of tantalum (Ta), and on the underlayer 1, a seed layer 2 made of a metal, such as chromium (Cr), having a body-centered cubic (bcc) structure is formed.
On the seed layer 2, an antiferromagnetic layer 3, a pinned magnetic layer 4, a nonmagnetic material layer 5, a free magnetic layer 6, and a protective layer 7 are successively formed in that order, thereby forming a multilayer film T.
The protective layer 7 is formed of Ta, the nonmagnetic material layer 5 is formed of copper (Cu), the free magnetic layer 6 and the pinned magnetic layer 4 are formed of a NiFe alloy, and the antiferromagnetic layer 3 is formed of PtMn.
On the top and the bottom of the multilayer film T, electrode layers 10 are provided, and a sense current is allowed to flow in a direction perpendicular to the film surface of the multilayer film.
An exchange coupling magnetic field is generated at the interface between the antiferromagnetic layer 3 and the pinned magnetic layer 4, and the magnetization of the pinned magnetic layer 4 is pinned in a height direction (Y direction in the figure).
At two sides of the free magnetic layer 6, hard bias layers 8 made of a hard magnetic material such as CoPt are formed, and the top, the bottom, and the end of each of the hard bias layers 8 are insulated by an insulating layer 9. By a longitudinal bias magnetic field applied from the hard bias layers 8, the magnetization of the free magnetic layer 6 is aligned in a track width direction (X direction in the figure).
When an exterior magnetic field is applied to the magnetic sensor shown in FIG. 7, the magnetization direction of the free magnetic layer is relatively changed with respect to that of the pinned magnetic layer, and as a result, the resistance of the multilayer film is changed. When a constant sense current flows, the exterior magnetic field is detected by detecting this change in resistance as the change in voltage.
As a material for forming the free magnetic layer and the pinned magnetic layer of a magnetic sensor, a permalloy has been often used. For example, a magnetic sensor which uses a NiFe alloy other than a permalloy for forming the free magnetic layer and the pinned magnetic layer has been disclosed in Japanese Unexamined Patent Application Publication No. 2002-204010.
The permalloy is a NiFe alloy containing 80 atomic percent of nickel (Ni). In addition, as described in paragraph (0023) of Japanese Unexamined Patent Application Publication No. 2002-204010, a NixFe(100-x) alloy (40≦x≦70) is used as a high spin polarization material.
However, even when the free magnetic layer and the pinned magnetic layer are formed using a NiFe alloy having the above composition, it has been difficult to obtain a product ΔR·A of 5 mΩ·μm2 or more, ΔR and A being the change in resistance and an element area, respectively, of a CPP-GMR type magnetic sensor in which a direct sense current is allowed to flow in a direction perpendicular to a film surface of a multilayer film, and as a result, a practical reproduction output cannot be obtained.